The world is currently experiencing revolutionary changes in communications systems, brought about, in part, by the general availability and evolution of wireless telephony systems. Immediately after the first mobile user headed off into the sunset with a cellular telephone, or Mobile Station (MS), however, someone else wondered where they went. Unlike conventional wireline telephones, wireless callers are not usually associated with a fixed location, which provides many benefits such as freedom of use over large geographical areas. Because the location of a MS is usually not fixed, it is necessary for the wireless telephony system to be able to determine where the MS is located so that calls can be properly routed to it.
In order to route a call to a MS that is outside of the home area of the subscriber's service provider, a roaming number must be used. When a call is made to a MS, a Gateway Mobile Switching Center (GMSC) sends a query to a Home Location Register (HLR) to determine how to route a call to the MS. The HLR keeps track of the approximate location of the MS within the wireless telephony network. The HLR requests a roaming number from the Mobile Switching Center serving the geographical area in which the MS is currently located. The HLR forwards the roaming number to the GMSC, which then uses the number to setup the call toward the serving MSC.
Roaming numbers are a MSC switch property; they belong to the MSC. Roaming numbers are public network numbers and are associated with a specific MSC; i.e., a call to a roaming number will always be routed to a specific MSC. Network operators assign a particular set of roaming numbers to each MSC switch so that terminating calls to a MS served by the MSC can be completed using one of the MSC's associated roaming numbers. The public network, e.g., the Public Switched Telephone Network (PSTN) or the Public Land Mobile Network (PLMN), uses a routing mechanism that routes calls to a particular MSC when a roaming number associated with that MSC is allocated to a call request to a MS within the service area of the MSC. A call setup request to a roaming number associated with a MSC is performed in the same manner as any ordinary call.
Because a call setup request to a roaming number is performed in the same manner as any ordinary call, it is possible for any person who discovers the roaming numbers associated with a MSC to place malicious calls to one or more of the roaming numbers associated with each MSC within a wireless network. A conventional MSC does not have any mechanisms to ensure that an incoming call request is, in fact, associated with a call request to a MS within the service area of the MSC. Accordingly, there is a need in the art for systems and methods to prevent unauthorized use of roaming numbers in a wireless telecommunications system.